Comparison of optimal design and performance of PM machines having non-overlapping windings and different rotor topologies

This paper investigates the influence of machine´s parameters on the design and optimisation of permanent magnet (PM) brushless ac machines having three different rotors, viz. surface PM (SPM), I-shaped interior PM (IPM-I) and V-shaped interior PM (IPM-V), and with non-overlapping double/single layer windings. The IPM-V angle δ between two magnet pieces within a pole was found to have a significant impact on the optimum split ratio. Smaller values of angle δ have smaller optimal split ratios and higher torque. However, for torque per magnet volume, a global optimal split ratio and angle δ can be found within limits. Increasing the magnet thickness for interior PM machines results in a decrease in the magnet width due to geometric limitations and hence there exists an optimal magnet thickness for maximum torque, which is obvious in IPM-V machines. Comparison reveals that the IPM-I machine presents the widest constant power-speed region due to its larger d-axis inductance and low back-EMF. Single layer windings produce larger average torque and d-axis inductance, hence wider power-speed range operation, however exhibits larger torque ripples.